This invention relates in general to the welding of aluminum and similar materials and, more specifically, to an improved back-up tape for use in such welding.
In butt welding thin sheets or structures together, a number of problems may be encountered. Welding such structures without support along the weld line opposite the welding head is generally unsatisfactory. Molten metal from the weld zone tends to drop through, leaving voids along the weld line. Also, the underside of the weld tends to be uneven, with droplet-like projections.
Attempts have been made to support weld lines with solid structures, which, while useful in some cases, are not adaptable to a variety of structure and sheet shapes. Tape-like support means of various kinds have also been used, adhesively bonded along the weld line. The surfaces of some back-up tapes are intended to fuse during the welding operation, and may include a surface layer of a flux. This type tape is undesirable in high quality aerospace-type applications where the weld must be free of contamination.
Other commercial tapes, while satisfactory for rough work or where the weld bead is to be finish machined, do not provide adequate support to produce highly uniform, smooth weld beads. In some cases, local failure of the tape from thermal weakening or melting will permit drop through of the fused metal, leaving insufficient metal to form a satisfactory bead, especially where no metal is added during welding.
In order to provide sufficient support, many tapes require a rigid back-up plate pressing the tape against the weld underbead. In welding complex structures, such as long tubes, it is inconvenient to attempt to hold the tape in place with a solid member. Since the solid backing member must conform to the surface being welded, a special backing member must be built for each structure design being welded.
Other backing strips or tapes may include a metal or solid refractory strip to provide rigid support. These tapes are complex, heavy, difficult to install and will conform to curved weld surfaces of only large radii of curvature.
Thus, there is a continuing need for improved welding back-up tapes especially for use in welding aluminum to high quality standards.